Solar panels on field up close
In Dronninglund, Denmark, the district heating company has established solar panels covering an area equal to nearly nine football fields.

Thermal energy storage

Great potential in new solar technology

The Dronninglund district heating company in Denmark has created one of the world’s largest solar heating systems. A reservoir of 91 by 91 metres (300 by 300 feet) stores the summer heat, so the company can use it for district heating supply during winter.

Solar panels with a combined size of nearly nine football fields, and a thermos with a capacity of 25 Olympic sized swimming pools. That is the simplified recipe for a huge solar heating system, which opened in 2014. The facility delivers half of the thermal energy consumption used by the 1,300 district heating customers in Dronninglund, which is a city in the northern part of Jutland in Denmark.

NIRAS was the technical consultant, and PlanEnergi has been the client's consultant for the ambitious facility now owned by the Dronninglund district heating company. The facility combines a range of different and innovative technologies in a brand new solution. The solution is based on an improved and further developed version of the existing storage technology. The new ways of combining technologies hold a massive potential.

Saves heat from the summer sun

Regardless of the source of energy in question, the storage technology can be used anywhere where there is a gap between the production of heat and when that heat is required.

We can store heat from the summer months and use it for district heating during winter. The technology can also be used in connection with unstable energy sources such as wind energy. In addition, the technology can be used to utilise excess heat from electricity production, waste incineration, and industrial processes. The thermal energy storage in Dronninglund has been named Sunstore.

During the summer months, the large area with solar collectors will ensure that the water temperature in the 61,700 m3 (16.2 million gallons) reservoir reaches about 90°C (195°F).

During the winter, the temperature will fall below the supply temperature needed in the district heating network, but by using heat pumps, the water can be heated sufficiently to be used for district heating. When spring arrives and the sun returns, the temperature in the thermal energy storage will drop to below 10°C (50°F) – depending on the temperature during the winter months.

Fixed price on district heating the following 25 years

The Danish Energy Agency granted the project funding of 3 million Euro (USD 3,100,000). The great potential of the technology is emphasized by the immense global interest in the results of the development of the new technologies.

Because of the usage of the solar heating system, the price on district heating from Dronninglund district heating company will be fixed the next 25 years. It is an independent system, that does not rely on world prices of oil and gas. Compared to biomass and natural gas, the operational costs of the system are very modest. Solar heat is even CO2 neutral.